The present invention relates to engines, and particularly to a differential engine with variable torque conversion.
A major problem with existing electric engines is that the peak efficiency occurs over a relatively narrow range of output speeds, which are not at low or starting speeds. An efficiency-speed curve for a typical engine is shown in FIG. 1 and indicated by reference A. As shown in FIG. 1, the typical electric engine achieves peak efficiency in the range of 80% to something less than 100% and is represented by point B on the efficiency-speed curve A, whereas a low output speeds and startup speeds (indicated by reference C), the efficiency is in the range 20 to 25%.
This problem is compounded by the need for high starting torque if a load, for example, an automobile, has to reach operating speed under acceleration. The starting torque varies directly with acceleration - the higher the acceleration, the higher the required starting torque. As torque is directly proportional to the current in the motor coil, the accelerating torque (e.g. acceleration from a stopped position or deceleration under a controlled reverse motor torque) will demand a significantly higher motor coil current. This means the current required by the motor to produce a given torque at a low speed or from a stop will be much greater than the current that would be needed to produce the same torque at higher speeds because the efficiency of the motor at low speeds is much less than at higher speeds as illustrated by points B and C on the efficiency vs. output-speed in FIG. 1. Furthermore, the energy loss in the motor increases exponentially as this loss is equal to the resistance of the motor winding multiplied by the current raised to the second power.
During stop/start operation of an electric motor powered system, particularly when relatively quick acceleration and deceleration forces are present, the operating efficiency of the electric motor will be well below the peak efficiency point, and is typically in the range of 20% to 25% as indicated by point C in FIG. 1, even lower than this under accelerating/decelerating conditions. As a result, an electric vehicle will travel much farther distances at constant highway driving conditions than within a city.
In view of these and other known deficiencies, there remains a need for an engine which improves on the torque output vs. speed characteristic of known designs and approaches the ideal engine operating characteristic as shown in FIG. 1(b).
The present invention provides a differential engine with variable torque conversion.
In a first aspect, the present invention provides, a differential engine with a variable torque output, the differential engine comprises: (a) a motor for driving an output shaft at a rotational speed and applying an input rotational torque to said output shaft; (b) a torque conversion stage coupled to the motor for converting the input rotational torque into a rotational torque at an output shaft for coupling to a load; (c) the torque conversion stage including a first differential stage, the first differential stage having an input shaft coupled to the output shaft of the motor, and the first differential stage having a gear mechanism for translating the rotational torque from the input shaft to first and second output shafts and the gear mechanism driving each of the output shafts at the same speed and in opposing rotational directions; (d) the torque conversion stage including a second differential stage, the second differential stage having a first input shaft coupled to the first output shaft of the first differential stage, and a second input shaft coupled to the second output shaft of the first differential stage, and including a gear mechanism for applying a rotational torque to the output shaft when a difference occurs between the rotational speeds of the first and second input shafts for the second differential stage; (e) a loading mechanism, the loading mechanism being coupled to one of the input shafts on the second differential, the loading mechanism being responsive to a control input for loading the input shaft to vary the rotational speed of the associated input shaft.
In another aspect, the present invention provides a differential engine with a variable torque output, the differential engine comprises: (a) a motor for driving an output shaft at a constant speed in a predetermined direction; (b) a transmission stage having an input shaft and an output drive shaft for driving a load, the input shaft is coupled to the output shaft of the motor; (c) a regenerative charging stage, the regenerative charging stage has an input for receiving power from the transmission stage and charging an energy storage device; (d) the transmission stage comprises a first differential stage and a second differential stage, the first differential stage has a drive mechanism coupled to the input shaft, and the second differential stage has a drive mechanism coupled to the output drive shaft, and the drive mechanism for the first differential stage is coupled to the drive mechanism for the second differential stage through first and second differential shafts, the differential shafts rotate in opposite directions at the same speed; (e) the transmission stage includes a generator coupled to one of the differential shafts, the generator is responsive to a control input for generating the power output for the regenerative charging stage, and operation of the generator loads the differential shaft and produces a difference in the speed of the differential shafts, and the drive mechanism in the second differential stage translates the difference to the rotational speed of the output drive shaft.
In yet another aspect, the present invention provides a differential engine with a variable torque output, the differential engine comprises, (a) a first motor for driving an output shaft at a rotational speed and applying an input rotational torque to the output shaft; (b) a second motor for driving an output motor shaft at a rotational speed and in a same direction as the output shaft for the first motor; (c) a torque conversion stage coupled to the motor for converting the input rotational torque from the first motor and the second motor into a rotational torque at an output drive shaft for coupling to a load; (d) the torque conversion stage includes a first differential stage, the first differential stage has an input shaft, the first differential stage has a gear mechanism for translating the rotational torque from the input shaft to first and second output shafts and the gear mechanism driving each of the output shafts at the same speed and in opposing rotational directions; (e) the torque conversion stage including a second differential stage, the second differential stage has a first input shaft coupled to the first output shaft of the first differential stage, and a second input shaft coupled to the second output shaft of the first differential stage, and including a gear mechanism for applying a rotational torque to the output drive shaft when a difference occurs between the rotational speeds of the first and second input shafts for the second differential stage; (f) an input stage having a first input shaft coupled to the output shaft of the first motor, and a second input shaft coupled to the output motor shaft of the second motor, and the input stage having an output shaft and the output shaft being coupled to the input shaft of the first differential stage, and the input stage including a gear mechanism for translating the rotational torque from the output motor shaft and the output shaft to the output shaft of the input stage; (g) a loading mechanism, the loading mechanism is coupled to one of the input shafts on the second differential stage, the loading mechanism is responsive to a control input for loading the input shaft to vary the rotational speed of the associated input shaft.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.